Halogenated aromatic polyesters such as the condensation products of 4,4'-isopropylidene-2,2',6,6'-tetrachlorodiphenol or 4,4'-isopropylidene-2,2',6,6'-tetrabromodiphenol with isophthalic acid and/or terephthalic acid or the esterforming derivatives thereof are known and may be prepared, for example, by acid interchange reactions as disclosed, e.g., in U.S. Pat. Nos. 3,948,856 and 3,824,213, both of which are assigned to the assignee of the present invention.
Another method for preparing these halogenated aromatic polyesters in the solution polymerization process as disclosed in U.S. Pat. No. 3,234,167 which is hereby incorporated by reference. This method involves the reaction in solution of the halogenated aromatic alcohol with an excess of an acid acceptor which is typically a tertiary amine such as triethyl amine and then the reaction of the tertiary amine/halogenated aromatic alcohol complex with isophthaloyl halide and/or terephthaloyl halide to produce a reaction mixture comprising solvent, the halogenated aromatic polyester, tertiary amine hydrochloride, and unreacted tertiary amine. The unreacted tertiary amine is then neutralized with aqueous hydrochloric acid to form a two-phase system. See, for example, U.S. Pat. No. 3,864,448, which is assigned to the assignee of the present invention.
Although this neutralization technique is effective in converting substantially all of the tertiary amine into the hydrochloride of the tertiary amine, it suffers from the disadvantages that (1) a substantial excess of hydrochloric acid is required to neutralize all of the tertiary amine if neutralization is to be accomplished in a commercially acceptable period of time, and (2) if a substantially stoichiometric amount of hydrochloric acid is employed (i.e., substantially no excess), then the two-phase system must be in contact for a commercially unacceptable period of time for substantially complete neutralization to take place.
Also, the two-phase prior art method of neutralizing the tertiary amine necessarily dilutes the tertiary amine/hydrochloride complex which is already formed (by the reaction of the isophthaloyl halide and/or terephthaloyl halide with the complex of halogenated aromatic alcohol and tertiary amine) and also dilutes that tertiary amine hydrochloride which is formed during the neutralization reaction. Such dilution is disadvantageous since the tertiary amine hydrochloride must be separated from the solvent and the addition of water in the aqueous hydrochloric acid solution tends to render the water removal process more difficult.
Finally, the two-phase prior art method of neutralizing the tertiary amine generally requires four sequential aqueous hydrochloric acid washes to effect the substantial removal of the tertiary amine hydrochloride. Each neutralization step involves agitation, settling and decantation, followed by three or more water washes to achieve a pH of 6. Furthermore, transfer of the excess tertiary amine to the interface of the two phase system and contact of the tertiary amine with the hydrochloric acid in the aqueous phase all involves significant amounts of time. These time requirements are disadvantageous, especially in a commercial process.
The search has continued for improved processes for producing halogenated aromatic polyesters. This invention was made as a result of that search.